C by Ed Brothers. July 1998
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      Subroutine ROTATE
      implicit double precision(a-h,o-z)
#include "divcon.dim"
#include "divcon.h"

C The purpose of this segment is to calculate the energetic barrier to rotation
C of a molecule.

C  Variable declaration.

      dimension imove(maxatm-3),ifix(maxatm-3)
      integer counter
      character*80 string1, string2

C  Initialization block

      DO I=1,natoms-3
         imove(I)=0
         ifix(I)=0
      ENDDO

      counter=0

      DO i=1,npar
         DO j=1,2
            ipar(j,i)=0
         ENDDO
      ENDDO

      npar=0
      nstore=0
      maxval=natoms-3

C  Read in segment to be rotated.

      backspace inpt
      DO I=1,3
         read (inpt,fmt='(A80)') string1
         IF (index(string1,'ROT_END').ne.0) THEN
            continue
         ELSEIF (index(string1,'END_ROT').ne.0) THEN
            continue
         ELSEIF (index(string1,'ROT').ne.0) THEN
            read(inpt,fmt='(A80)') string2
            call atmlst(string2,maxval,imove,nstore,ierror)
         ELSEIF (index(string1,'CONDIH').ne.0) THEN
            read(inpt,fmt='(A80)') string2
            call atmlst(string2,maxval,ifix,nstore,ierror)
         ELSE
C-RDC             write(iout,'(/" ERROR: ELEMENTS FOR ROTATION ",
C-RDC      &           "ARE IMPROPERLY DEFINED")')
         ENDIF
      ENDDO

C  Find the value of the counter, which is the number of atoms that are to
C  be moved.


      DO I=1, maxval
         IF(imove(i).ne.0) counter=counter+1
      ENDDO

C Convert to z-matrix coordinates.  This is done primarily for ease in coding.

      call zmake
      call wrtint

C  Add user defined degree of rotation to dihedral of atoms to be rotated.
C  Tests are to ensure dihedral is between -pi and pi. (-180 to 180)

      DO I=1,counter
         zmat(3,imove(I))=zmat(3,imove(I))+rotang
         IF (zmat(3,imove(I)).gt.pi) zmat(3,imove(I))
     .      =-(2.d0*pi-zmat(3,imove(I)))
         IF (zmat(3,imove(I)).lt.-pi) zmat(3,imove(I))
     .      =2.d0*pi+zmat(3,imove(I))
      ENDDO

C  Turn off optimization flag for dihedral of fixed atoms in set to be
C  rotated.

      DO I=1, maxval
         IF (ifix(i).ne.0) iopt(3,ifix(i))=0
      ENDDO


C  Save original energy, then calculate new energy, and output rotional
C  barrier.

      call wrtint
      ebarr=eheat
      eheat=0.d0
      rotat2=.true.
      call edriver(ierror)
C-RDC       IF (ierror.eq.1) write (iout,
C-RDC      .   '("ERROR IN ROTATION MINIMIZATION")')
C-RDC       ebarr=eheat-ebarr
C-RDC       call wrtint
C-RDC       write (iout,980) ebarr
 980  format (/' BARRIER TO ROTATION  =',4x,F7.4)


1000  RETURN

      END